Substrate for display device having a protective layer provided between the pixel electrodes and wirings of the active matrix substrate and display device

ABSTRACT

A substrate for a display device includes a scan line, a signal line, a switching element provided on an insulating substrate, an interlayer insulation film, and a pixel electrode. The switching element is provided at an intersection of the scan line and the signal line. The switching element includes a gate electrode connected to the scan line, a source electrode connected to the signal line, and a drain electrode connected to the pixel electrode. The interlayer insulation film includes a contact hole for connecting the drain electrode of the switching element to the pixel electrode. A protective layer formed of an insulating material is provided without contact holes above the scan line and/or the signal line. A portion of an underlying film under the protective layer contacts a portion of an overlying film over the protective layer.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application is a Divisional of U.S. patentapplication Ser. No. 11/126,743, currently pending, which claimspriority under 35 U.S.C. §119(a) on Patent Application No. 2004-154506filed in Japan on May 25, 2004, the entire contents of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a substrate for a display device, amanufacturing method for the same, and a display device. Morespecifically, the present invention relates to a substrate for a displaydevice that can be applied to a liquid crystal display device and thelike, a manufacturing method for the same, and a display device that hassuch a substrate.

2. Description of the Related Art

At present, liquid crystal display devices have characteristics such ascompact, thin, lightweight, and low power consumption, and have beenwidely used in a variety of electronic apparatuses. In particular,active matrix type liquid crystal display devices (liquid crystaldisplay panels) having switching elements as active elements havedisplay properties of the same level as those of CRT's (cathode raytubes), and therefore, have been widely applied in OA apparatuses, suchas personal computers, AV apparatuses, such as television sets, andcellular phones. Such liquid crystal display devices recently have beenlarger and improved in qualities such as high-definition and improvementof effective area ratio of pixels (high aperture ratio) rapidly.Therefore, further improvement in the performance of substrates fordisplay devices used in display devices such as liquid crystal displaydevices has been required, and improvement in design, manufacturingtechnology and the like has progressed.

Active matrix substrates are widely used as substrates for displaydevices such as liquid crystal display devices. A manufacturingtechnology for an active matrix substrate where pixel electrodes andsource lines (signal lines) are formed on the same plane on a substrateis known, and in the case where an increase in the definition and theaperture ratio is achieved according to this technology, the distancebetween pixels and source lines, the width of source lines and the likehave been reduced, in order to increase the effective area of pixels.However, reduction of the distance between pixels and source lineseasily occurs defect of short-circuiting, and reduction of the width ofsource lines easily occurs defect of disconnected wirings. That is tosay, occurrence of defect of short-circuiting poses reduction in yieldaccording to a manufacturing technology for an active matrix where pixelelectrodes and source lines are formed on the same plane on a substrate,and there is room for improvement in this respect.

For this reason, manufacturing methods for a transmission type liquidcrystal display devices characterized by the following (a) to (c), forexample, have been proposed (for example, refer to Japanese KokaiPublication Hei-09-152625 (pages 1 to 3)) with respect to amanufacturing method for an active matrix substrate, in order to preventdefects caused by short-circuiting and disconnected wirings as describedabove, as well as in order to improve reduction of the yield.

(a) A (transparent) interlayer insulation film is provided afterswitching elements (active elements) and source wirings (source lines)have been formed.

(b) Switching elements are brought into connect with (transparent) pixelelectrodes through contact holes.

(c) Pixel electrodes are formed on the interlayer insulation film, andthereby, source wirings and pixel electrodes are not disposed on thesame plane.

A liquid crystal display device is manufactured by attaching a colorfilter substrate so as to face the active matrix substrate manufacturedas mentioned above and by injecting liquid crystal between thesesubstrates. As for the color filter substrate, a substrate where colorregions of R (red), G (green) and B (blue), for example, are provided soas to correspond to the pixel regions on the active matrix substrateside, and in addition, a black matrix (light blocking film) is providedin the portion other than the respective pixel regions, may be used.

FIG. 13 is a schematic plan diagram showing one pixel in an activematrix substrate (thin film transistor array substrate) according to theprevious art, and a portion of a pixel adjacent to the pixel. As shownin FIG. 13, the gate line (scan line) 101 and the source line (signalline) 102 are placed so as to cross each other in one pixel of an activematrix substrate 130. A thin film transistor (hereinafter referred toalso as TFT) 114, used as a switching element, and the pixel electrode103 are disposed in the crossing portion. The TFT 114 is formed of thegate electrode 104 connected to the gate line 101, the source electrode105 connected to the source line 102, the drain electrode 106 connectedto the pixel electrode 103, and the semiconductor layer 125 in islandform. The drain extracting-electrode 106′ is connected to the pixelelectrode 103 through a contact hole 109. In addition, the lead outdrain electrode 106′ faces a common capacitance line 107 with anintervening gate insulator 111, and thus, an auxiliary capacitor isformed.

Next, a manufacturing method for an active matrix substrate,particularly a thin film transistor array substrate, is brieflydescribed with reference to FIGS. 13 to 17. FIG. 14 is across sectionaldiagram of the thin film transistor array substrate along line H-H′ ofFIG. 13, and FIG. 15 is a cross sectional diagram of the thin filmtransistor array substrate along line I-I′ of FIG. 13. FIG. 16 is aschematic plan diagram showing terminals for leading out gate lines, andFIG. 17 is a schematic plan diagram showing terminals for leading outsource lines.

When a thin film transistor array substrate is manufactured, first, thegate lines (scan lines) 101, the gate electrodes 104 and the commoncapacitance lines 107 are simultaneously formed by means of filmformation, photolithography and etching on a substrate 110 made of atransparent insulating substrate, such as glass.

Next, thereon the gate insulator 111, the active semiconductor layer 112and the low resistance semiconductor layer 113 made of n type amorphoussilicon or the like are formed as films which are then converted to theisland form 125 by means of photolithography and etching.

Next, the source lines 102, the source electrodes 105, the drainelectrodes 106 and the lead out drain electrodes 106′ are,simultaneously formed by means of film formation, photolithography andetching, and subsequently, the low resistance semiconductor layer 113are separated into sources and drains through etching.

Next, the lower interlayer insulation film 120 made of SiNx or the likeare formed as films so as to cover the entire surface, and subsequently,the upper organic interlayer insulation film 115 made of aphotosensitive acryl resin or the like are formed by means ofphotolithography so as to have a pattern for contact holes 109, apattern for contacts of the terminals for leading out gate lines (X inFIG. 16), and a pattern for contacts of the terminals for leading outsource lines (Y in FIG. 17).

Next, the lower interlayer insulation film 120 and the gate insulator111 are sequentially etched by using the upper organic interlayerinsulation film 115 as a mask, in order to form the contact holes 109,the terminal for leading out gate line 200 and the terminal for leadingout source line 300.

Next, the pixel electrodes 103, the uppermost layer electrodes 201 ofthe terminal for leading out gate line 200, and uppermost layerelectrodes 301 of the terminal for leading out source line 300 areformed so as to cover the contact holes 109, the terminal for leadingout gate line 200 and the terminal for leading out source line 300. Thecontact holes 109 allow the drain electrodes 106 in TFT's 114 and thepixel electrodes 103 to be connected to each other through the lead outdrain electrodes 106′.

According to such a manufacturing method, the source lines 102 and thepixel electrodes 103 can be separated from each other with theintervening interlayer insulation films 115 and 120 in the active matrixsubstrate. Separation of the source lines 102 from the pixel electrodes103 can prevent reduction of the yield caused by short-circuitingbetween the pixel electrode 103 and the source line 102, and at the sametime, as shown in FIG. 13, the pixel electrodes 103 and the source lines102 can be overlapped, resulting in improvement in the aperture ratio ofthe liquid crystal display devices or the like.

According to the above described manufacturing method for a substratefor a display device, however, in the case where a defect on the upperorganic interlayer insulation film occurs, the lower interlayerinsulation film and the gate insulator are etched from the film defectportion and short-circuiting occurs in a pixel electrode formed on theupper organic interlayer insulation film and therefore, there is roomfor improvement in terms of preventing defects in display, reductions inthe quality of the display device, and in the yield.

A technology for making the gate insulating layer to have a two-layerstructure formed of an oxide insulating layer produced by oxidizing ametal film and a gate insulator has been proposed for a previoussubstrate for a display device (for example, refer to Japanese KokaiPublication Hei-03-153217 (pages 1 and 3)). When a gate insulating layerhas multiple layer structure according to this technology, however,effects of preventing defects of short-circuiting due to a defect on aninterlayer insulation film cannot be obtained, when the insulating filmexisting lower than the uppermost layer is removed by etching with theuppermost interlayer insulation film as a mask. In addition, thistechnology provides measures against the defect of the gate insulator,and does not provide measures against the defect of a pixel caused byelectrical leakage caused by the defect of the insulating film thatexists between wirings, such as gate lines and source lines, and pixelelectrodes in a substrate for a display device where the pixelelectrodes are formed on the interlayer insulation film.

SUMMARY OF THE INVENTION

The present invention is provided in view of the above described currentstate, and an object of the invention is to provide a substrate for adisplay device that makes it possible to obtain a display device of ahigh display quality with a high yield by preventing short-circuitingbetween a pixel electrode and wirings, such as a scan line or a signalline, particularly when a substrate for a display device having highdefinition and a high aperture ratio is manufactured, and amanufacturing method for the same, as well as a display device that usessuch a substrate.

The present inventors have, in a variety of manners, examined substratesfor display devices having high definition and high aperture ratios andwhich make it possible to obtain a display device having a high displayquality with a high yield, and have found that defect of film, such aspeeling of an (upper) interlayer insulation film located beneath a pixelelectrode may occur in a region where a wiring, such as a scan line(gate bus line) or a signal line (source bus line), and a pixelelectrode overlap in a plane (region where the two overlap as viewed inthe direction perpendicular to the surface of the substrate) in theconventional configuration of a substrate. The inventors focused on theoccurrence of defects of leakage in such a case, since a gate insulatoror the like in the defect portion is etched by using the (upper)interlayer insulation film as a mask for etching, and wirings, such asthe scan line or the signal line (source bus line) is exposed, and thenthe exposed wiring and the pixel electrode make contact with each otherby film forming and patterning of the pixel electrode. That is to say,when such a leakage occurs between the wiring and the pixel electrode, apotential written in a pixel cannot be maintained, leading to a pointdefect in the display. Therefore, inventors have found that providing aprotective layer above the wiring such as the scan line and the signalline (source bus line) as a protective layer against etching can preventcontact between the pixel electrode and the wiring, leading toprevention of a defect of leakage caused by such short-circuiting. Theinventors have found that, for example, a pattern of a semiconductorlayer to form a switching element is disposed on a region where the scanline and the pixel electrode overlap on a plane, and thereby, thissemiconductor layer pattern works as a protective film against etching,even when the interlayer insulation film is peeled, and thus, electricalleakage between the pixel electrode and the scan line can be preventedwithout increasing the number of steps in the manufacturing process fora substrate, and it becomes possible to provide a display device such asa liquid crystal display device having a high definition and a highaperture ratio with a high yield, and in this manner, means that cancompletely solve the above described problem are provided, leading tothe completion of the present invention.

That is to say, the present invention provides a substrate for a displaydevice, comprising a scan line, a signal line and a switching element onan insulating substrate, and further comprising an interlayer insulationfilm and a pixel electrode, wherein the switching element is provided atan intersection of the scan line and the signal line, and have a gateelectrode connected to the scan line, a source electrode connected tothe signal line, and a drain electrode connected to the pixel electrode,the interlayer insulation film has a contact hole for connecting thedrain electrode of the switching element to the pixel electrode, and aprotective layer is provided above the scan lines and/or the signallines in the substrate for a display device.

The present invention also provides a substrate for a display device,comprising a scan line, a signal line, a common capacitance wiring and aswitching element on an insulating substrate, and further comprising aninterlayer insulation film and a pixel electrode, wherein said theswitching element is provided at a intersection of the scan line and thesignal line, and have a gate electrode connected to the scan line, asource electrode connected to the signal line, and a drain electrodeconnected to the pixel electrode, the interlayer insulation film has acontact hole for connecting the drain electrode of the switching elementto the pixel electrode, and a protective layer is provided above atleast one of wirings selected from the group consisting of the scanline, the signal line and the common capacitance wiring in the substratefor a display device.

Other features, elements, processes, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of preferred embodiments of the presentinvention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional diagram showing an example of across sectional configuration of a liquid crystal display deviceaccording to the present invention (Embodiment 1);

FIG. 2 is a schematic plan diagram showing one pixel in an active matrixsubstrate (substrate for a display device) according to the presentinvention (Embodiment 1);

FIG. 3 is a cross sectional diagram of the substrate for a displaydevice along line A-A′ of FIG. 2;

FIG. 4 is a cross sectional diagram of the substrate for a displaydevice along line B-B′ of FIG. 2;

FIG. 5 is a schematic plan diagram showing one pixel in an active matrixsubstrate (substrate for a display device) according to the presentinvention (Embodiment 2);

FIG. 6 is a cross sectional diagram of the substrate for a displaydevice along line C-C′ of FIG. 5;

FIG. 7 is a cross sectional diagram of the substrate for a displaydevice along line D-D′ of FIG. 5;

FIG. 8 is a schematic plan diagram showing one pixel in an active matrixsubstrate (substrate for a display device) according to the presentinvention (Embodiment 3);

FIG. 9 is a cross sectional diagram of the substrate for a displaydevice along line E-E′ of FIG. 8;

FIG. 10 is a cross sectional diagram of the substrate for a displaydevice along line F-F′ of FIG. 8;

FIG. 11 is a schematic plan diagram showing an active matrix substrateaccording to the previous art in the state where the upper interlayerinsulation film is peeled and leakage is caused between a pixelelectrode and a gate line at leak point 800;

FIG. 12 is a schematic cross sectional diagram showing the cross sectionof leak point 800 along line G-G′ of FIG. 11;

FIG. 13 is a schematic plan diagram showing one pixel in an activematrix substrate (thin film transistor array substrate) according to theprevious art, and a portion of a pixel that is located adjacent to thispixel;

FIG. 14 is a cross sectional diagram of the substrate for a displaydevice along line H-H′ of FIG. 13;

FIG. 15 is a cross sectional diagram of the substrate for a displaydevice along line I-I″ of FIG. 13;

FIG. 16 is a schematic plan diagram showing terminals for leading outgate lines of a display device substrate to the outside; and

FIG. 17 is a schematic plan diagram showing terminals for leading outsource lines of a display device substrate to the outside.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A substrate for a display device according to the present invention haseither (A) a configuration where a scan line, a signal line and aswitching element are provided on an insulating substrate, and inaddition, an interlayer insulation film and a pixel electrode areprovided, or (B) a configuration where a scan line, a signal line, acommon capacitance wiring and a switching element on an insulatingsubstrate, and in addition, an interlayer insulation film and a pixelelement are provided. The above mentioned configuration (A) preferablyhas a layered structure having (1) the insulating substrate, (2) thescan line, the signal line and the switching element, (3) the interlayerinsulation film, and (4) the pixel electrode, in this order, andspecifically, has the configuration in which the signal line and thescan line are provided on the insulating substrate, each intersectionwhere the signal line and the scan line cross has the switching elementand the pixel electrode, the interlayer insulation film is providedabove the signal line, the scan line and the switching element, and thepixel electrode are provided on the interlayer insulation film. Theabove-mentioned configuration (B) preferably has a layered structurehaving (1) the insulating substrate, (2) the scan line, the signal line,the common capacitance wiring and the switching element, (3) theinterlayer insulation film, and (4) the pixel electrode or the like, inthis order.

The above described switching element is provided at the intersection ofthe scan line and the signal line, and have the gate electrode connectedto the scan line, the source electrode connected to the signal line, andthe drain electrode connected to the pixel electrode. And a gateinsulator is usually formed between the scan line (gate electrode) andthe signal line (source electrode), as well as between the scan line(gate electrode) and the drain electrode. In addition, the interlayerinsulation film has a contact hole for connecting the drain electrode ofthe switching element to the pixel electrode.

The substrate for a display device according to the present inventionhas such a configuration, and thereby, can carry out driving control ofthe switching element by means of currents (gate signal) to flow throughthe scan line, and at the same time, carry out driving control of thepixel electrode by means of currents (data signals) to flow through thesignal line when the switching element is in the ON state, and inaddition, the interlayer insulation film is provided in order to preventthe pixel electrode and the signal line from being short-circuited.

According to the present invention, the protective layer is providedabove the scan line and/or the signal line in the above describedconfiguration (A), and the protective layer is provided above at leastone of wirings selected from the group consisting of the scan line, thesignal line and the common capacitance wiring in the above configuration(B). That is to say, according to the present invention, the protectivelayer is provided above at least one of the scan line, the signal lineor the common capacitance wiring. As a result of this, the protectivelayer functions as a protective film against etching when etching iscarried out in order to form the contact hole in the interlayerinsulation film, and therefore, the wirings, such as the scan line, canbe prevented from being exposed after etching, even in the case where aportion of the pattern of the interlayer insulation film used as anetching mask has defect. Consequently, contact between the pixelelectrode on the interlayer insulation film and wirings, such as thescan line, can be prevented, and thus, short-circuiting can beprevented, and therefore, the occurrence of a defect in a pixel can beprevented, leading to improvement in the display quality and the yieldobtained particularly at the time of manufacturing a substrate for adisplay device having high definition and a high aperture ratio.

The material, thickness and the like of the above described protectivelayer are not particularly limited, as long as working effects ofprevention of exposure in wirings, such as the scan line, at the time ofetching of the interlayer insulation film can be obtained. Also, theprotective layer may be formed of the same material as that of anotherlayer adjacent, such as the interlayer insulation film or the gateinsulator, as long as the protective layer can protect the lower portionat the time of etching, and in such a case, when the protective layerand the other layers adjacent thereto are integrated with each other inthe cross section, and therefore to determine the border between thelayers is difficult, confirmation of difference in the plan form betweenthe protective layer and the other layers adjacent thereto that is tosay, the difference in the thickness between the integrated portion(protective layer+other layers adjacent thereto) and the portion notintegrated (only protective layer or only other layers adjacent thereto)enables determination of the protective layer.

In addition, according to the present invention, “a protective layer isprovided above” means that the protective layer may be provided on topof the wirings, such as the scan line, so as to contact with thewirings, such as the scan line, or that the protective layer may beprovided above wirings such as the scan line via one or more layers, soas not to contact with the wirings, such as the scan line. As for a modewhere a protective layer is provided so as not to make contact with thescan line, for example, mentioned may be a mode where the protectivelayer is provided on the gate insulator, a mode where the protectivelayer is provided in the interlayer insulation film and the like.

Next, described is the material of each component other than theprotective layer to form the substrate for a display device according tothe present invention.

For the insulating substrate, those made of a transparent insulator,such as glass, are preferably used.

The material of the scan line, the signal line and the commoncapacitance wiring is not particularly limited, as long as the desiredwiring resistance can be obtained, and mentioned may be metals, such astantalum (Ta), titanium (Ti), chromium (Cr) and aluminum (Al), alloysthereof and layered film, such as Ti/Al/Ti, where these metals arelayered. The width, the thickness, the pattern forms and the like of thescan line, the signal line and the common capacitance wiring are notparticularly limited.

The switching element is not particularly limited as long as they havethe gate electrode, the source electrode and the drain electrode, andmentioned may be an amorphous silicon thin film transistor, amicrocrystal silicon thin film transistor, a polysilicon thin filmtransistor, CGS (Continuous Grain Silicon) thin film transistor and thelike. In addition, the gate electrode is usually formed so as to beintegrated with the scan line, and the source electrode and the drainelectrode are formed so as to be integrated with the signal line.

The material of the interlayer insulation film is not particularlylimited, as long as the desired dielectric constant, transmittance,etching selective ratio and the like can be obtained, and mentioned maybe silicon nitride (SiNx), a photosensitive transparent resin, siliconoxide (SiO₂) and the like. Examples of the photosensitive transparentresin that may be used for the interlayer insulation film include, forexample, an acryl based resin, an epoxy based resin, a polyurethanebased resin, a polyimide based resin and the like. The interlayerinsulation film may be formed of one layer or two or more layers, andthe thickness thereof is not particularly limited.

The contact hole formed in the interlayer insulation film is notparticularly limited, as long as the drain electrodes of the switchingelement may be connected to the pixel electrode thereby, and the shape,size, number, arrangement and the like thereof are not particularlylimited. A conductive film for making electrical connections between thedrain electrodes of the switching elements and the pixel electrodes isusually formed within the contact hole.

For the material of the pixel electrode, preferably used may betransparent conductive materials, such as ITO (indium tin oxide), IZO(indium zinc oxide) and the like, and in the case of a substrate for adisplay device used for a reflective type liquid crystal display devicesor the like, metals, such as aluminum and silver, also may be preferablyused.

The configuration of the substrate for a display device according to thepresent invention is not particularly limited, as long as it has thesecomponents as essential components, and other components may be includedor not included.

The substrate for a display device according to the preferredembodiments of the present invention is hereinafter described in detail.

The above described protective layer is preferably provided beneath theinterlayer insulation film. As a result of this, when etching is carriedout for formation of the contact hole in the interlayer insulation film,the protective layer can function as a protective film against etching,and easier formation of the protective layer is possible as comparedwith a mode where the protective layer is formed in the interlayerinsulation film.

In addition, according to the present invention, “beneath the interlayerinsulation film” means on the underside of the interlayer insulationfilm or below the interlayer insulation film by one or more layers, andspecifically, a mode where the protective film for the scan line isprovided on the gate insulator may be provided, or a mode where theprotective layer for the scan line is provided on top of the scan lineso as to contact with the scan line.

The above described protective layer is preferably formed of asemiconductor, and preferably has substantially the same composition asthat of the semiconductor layer to form the switching element. In such acase, the formation of the protective layer can be simultaneouslycarried out as the formation of the semiconductor layer to form theswitching element, and therefore, the substrate for a display deviceaccording to the present invention may be manufactured without adding aforming process for the protective layer to the manufacturing processfor a substrate for a display device according to the previous art,resulting in shortening of the manufacturing process. For thesemiconductor, a semiconductor to form the semiconductor layer of theswitching element is preferable, and specifically, a semiconductor thatis formed primarily of amorphous silicon may be mentioned.

And “substantially the same composition” preferably has a component thatcan be evaluated to have substantially the same component, and thecomponent may be sufficient as long as the formation of thesemiconductor layer to form the switching element and that of theprotective layer can be simultaneously carried out in accordance with aCVD (chemical vapor deposition) method or the like.

The above described protective layer is preferably separated from thesemiconductor layer to form the switching element. As a result of this,even in the case where leakage occurs between the protective layer(semiconductor layer) provided above the scan line and the signal lineadjacent to the switching element and connected to the switchingelement, electrical leakage between the scan line and the drainelectrode connected to the switching element can be prevented, andtherefore, the occurrence of a defect in a pixel can be prevented.

The above described protective layer is preferably formed of siliconnitride (SiNx), silicon dioxide (SiO₂) or a resin. As a result of this,the protective layer can effectively function as a sufficient protectivefilm against etching, when etching is carried out, for example, for theformation of the contact hole in the interlayer insulation film, and theformation of the protective layer can be easily carried out. As for theresin, a photosensitive transparent resin is preferable, because of easeof patterning. Examples of the photosensitive transparent resin that canbe used for the protective layer include an acryl based resin, an epoxybased resin, a polyurethane based resin and a polyimide based resin. Inthe case where a material other than a photosensitive resin is used forthe protective layer, patterning may be carried out by film formation,application of photosensitive resin in liquid form and thenphotolithography (exposure to light and development), dry etching andthe like.

The above described protective layer preferably has substantially thesame composition as that of the source electrodes and/or the drainelectrodes to form the switching element. In such a case, the formationof the protective layer can be carried out simultaneously with theformation of the source electrode or the drain electrode to form theswitching element, and therefore, the substrate for a display deviceaccording to the present invention may be manufactured without adding aforming process for the protective layer to the manufacturing processfor a substrate for a display device according to the previous art, andthus, shortening of the manufacturing process can be achieved.

And “substantially the same composition” preferably means a componentthat can be evaluated to have substantially the same component, thecomponent may be sufficient as long as the formation of the sourceelectrode and/or the drain electrode to form the switching element andthat of the protective layer can be simultaneously carried out.

The above described protective layer is preferably disposed at least inportions where the scan line and the pixel electrode overlap as viewedin the direction perpendicular to the surface of the insulatingsubstrate. As a result of this, exposure of the scan line due to etchingmay be sufficiently prevented, and thus, the working effects of thepresent invention of preventing short-circuiting between pixel electrodeand scan line may be sufficiently obtained. More preferred is a mode inwhich the protective layer is disposed only in a portion where the scanline and the pixel electrode substantially overlap as viewed in thedirection perpendicular to the surface of the insulating substrate. Inthis mode, the working effects of the present invention of preventingshort-circuiting between pixel electrode and scan line can besufficiently obtained, and at the same time, an increase in the loadcapacitance of the scan line can be restricted to the minimum, andreduced, as compared with a case where, for example, the protectivelayer is provided so as to completely cover the scan line.

Additionally, the above description of “as viewed in the directionperpendicular to the surface of the insulating substrate” means, inother words, “when the orthogonal projection of the object is viewed onthe surface of the insulating substrate.” More specifically, it means“when the collection of the intersections between the surface of theinsulating substrate and lines perpendicular to the surface drawn fromrespective points on the object is viewed.” Accordingly, in this case,it means that the orthogonal projection of the scan line on the surfaceof the insulating substrate, the orthogonal projection of the protectivelayer and the orthogonal projection of the pixel electrodes overlap. Inaddition, the above description of “the portion where the scan line andthe pixel electrode substantially overlap” preferably means the portionthat is evaluated as a portion where the scan line and the pixelelectrode substantially overlap, but may include the peripheral portionsthereof, as long as the effects of restricting an increase in the loadcapacitance of the scan lines to the minimum may be obtained.

The above described protective layer is preferably disposed so as tooverlap the scan line and not to overlap the signal line as viewed inthe direction perpendicular to the surface of the insulating substrate.As a result of this, the occurrence of leakage between scan line andsignal line may be prevented, in the case where the protective film isformed of a semiconductor.

It is preferable for the above described interlayer insulation film tobe formed of an insulating film having at least two layers, and for theuppermost layer of insulating film to be an organic film. As a result ofthis, etching can be carried out by using the organic film which is theuppermost layer to form the interlayer insulation film as a mask, andthe efficiency of the manufacture of a substrate may be improved, ascompared with a case where a mask is separately formed on the interlayerinsulation film and removed after etching, or a case where etching iscarried out using the entire interlayer insulation film as a mask.

The organic film is not particular limited, as long as it is made of amaterial that can obtain the desired dielectric constant, transmittance,etching selective ratio and the like, and is appropriately selecteddepending on the etching condition and the like, and mentioned may be aphotosensitive transparent resin, such as an acryl based resin, an epoxybased resin, a polyurethane based resin and a polyimide based resin.

The present invention also provides a manufacturing method for formingthe substrate for a display device according to the present inventionhaving substantially the same composition as that of a semiconductorlayer that forms the switching element, said manufacturing method forthe substrate for a display device has a process for simultaneouslyforming the protective layer and the semiconductor layer that forms theswitching element. The present invention further provides amanufacturing method for forming the substrate for a display deviceaccording to the present invention having substantially the samecomposition as that of the source electrode and/or the drain electrodethat form the switching element, said manufacturing method for thesubstrate for a display device has a process for simultaneously forminga protective layer and source electrode and/or drain electrode that formthe switching elements. According to these methods, the substrate for adisplay device according to the present invention may be manufacturedwithout adding a forming process for the protective layer to themanufacturing process for a substrate for a display device according tothe previous art, and thus, shortening of the manufacturing process canbe achieved.

The present invention further provides a manufacturing method for asubstrate for a display device according to the present invention havingan interlayer insulation film formed of at least two layers ofinsulating film, and the top layer thereof is an organic film, saidmanufacturing method for the substrate for a display device has aprocess for simultaneously forming the contact hole, a terminal forleading out the scan line and a terminal for leading out the signal lineby carrying out etching using the organic film of the top layer thatforms the interlayer insulation film as a mask. As a result of this, andthe efficiency of the manufacture of the substrate may be improved, ascompared with a case where a mask is separately formed on the interlayerinsulation film and removed after etching, or a case where etching iscarried out using the entire interlayer insulation film as a mask. Inaddition, the efficiency in the manufacture of a substrate also may beimproved by simultaneously forming the terminal for leading out the scanline and the terminal for leading out the signal line in forming processof the contact hole.

Additionally, the contact hole in the organic film of the uppermostlayer are formed in advance at the time of formation of the organicfilm, and therefore, the contact hole in the portion other than theorganic film of the uppermost layer are formed by etching in the abovedescribed forming process of the contact hole.

The present invention also provides a display device with a substratefor a display device according to the present invention, or a substratefor a display device manufactured by the manufacturing method for asubstrate for a display device according to the present invention. Thedisplay device is not particularly limited, as long as the display canbe controlled by supplying electrical signals to the scan line, thesignal line and the like on the substrate for the display device.Examples of such a display include a liquid crystal display device, anorganic electroluminescence (EL) display or the like, and in particular,a liquid crystal display is preferable. In such a display, the pixelelectrode and wirings, such as scan lines, are prevented fromshort-circuiting, and the occurrence of a pixel defect is effectivelyprevented, and therefore, satisfactory display quality with fewer pixeldefects can be obtained even if the display device has high definitionand high aperture ratio, and the yield may be improved.

A substrate for a display device according to the present invention hasa configuration where the pixel electrode are provided on a differentplane from the plane where the scan line, the signal line and theswitching element are formed, and the protective layer is provided abovewirings, such as the scan line, and therefore, the occurrence of thepixel defect caused by short-circuiting between the pixel electrode onthe interlayer insulation film and wirings, such as the scan line, maybe prevented. In the case where such a substrate for a display device isused for a display device, satisfactory display quality with fewer pixeldefects can be obtained in the display device particularly having highdefinition and a high aperture ratio may be obtained, and effect ofimproved yield may be obtained.

The present invention will be, hereinafter, described in more detailwith reference to embodiments, the present invention is not limited toonly these embodiments.

Embodiment 1

Embodiment 1, which is one embodiment of the present invention, isdescribed below, with reference to FIGS. 1 to 4.

And according to the present embodiment, an active matrix substrate fora liquid crystal display device is described as a specific example of asubstrate for a display device.

FIG. 1 is a schematic cross sectional diagram showing one example of theconfiguration of a liquid crystal display device according to thepresent invention.

As shown in FIG. 1, the liquid crystal display devices 40 has the activematrix substrate (substrate for a display device) 30 and the facingsubstrate 33 having the color filter 34 and the light blocking film 35,and these substrates sandwich the liquid crystal layer 32. The liquidcrystal layer 32 is placed between the orientation film (not shown) ofthe facing substrate 33, and the orientation film (not shown) of theactive matrix substrate 30.

FIG. 2 is a schematic plan diagram showing one pixel inactive matrixsubstrate 30 of the present invention. FIG. 3 is a cross sectionaldiagram showing the substrate for a display device along line A-A′ ofFIG. 2, and FIG. 4 is a cross sectional diagram showing the substratefor a display device along line B-B′ of FIG. 2.

As shown in FIG. 2, in the active matrix substrate 30, the gate line(scan line) 1, the source line (signal line) 2 and the pixel electrode 3are formed as layers on the insulating substrate 10. The gate line 1 andthe source line 2 are disposed so as to cross to each other. Theswitching element (TFT) 14 and the pixel electrode 3 are provided ateach intersection of these lines. And the insulating substrate 10 ispositioned as the backmost layer of FIG. 2 and disposed at the positionshown in the cross sectional diagrams of FIGS. 3 and 4. The gateelectrode 4 of the switching element 14 is formed on the gate line 1,and the source electrode 5 of the switching element 14 is formed on thesource line 2. And the pixel electrode 3 is connected to the drainelectrode 6 of the switching element 14 through the lead out drainelectrode 6′. This lead out drain electrode 6′ faces the auxiliarycapacitor bus line 7 with the intervening gate insulator 11, andthereby, an auxiliary capacitor is formed.

As shown in FIG. 4, the active matrix substrate 30 is provided with theprotective film (protective layer) 8 on the gate insulator 11 so as tocover the surface of the gate line 1. As shown in FIG. 2, the activematrix substrate 30 has the region where the gate line 1, the protectivefilm 8 covering the surface of the gate line 1, and the pixel electrode3 overlap as viewed in the direction perpendicular to the surface of theinsulating substrate 10, that is, a region where the orthogonalprojection of the gate line 1 on the surface of the insulating substrate10, the orthogonal projection of the protective film 8 on the surface ofthe insulating substrate 10, and the orthogonal projection of the pixelelectrode 3 on the surface of the insulating substrate 10 overlap.

Next, control of current and voltage in the liquid crystal displaydevices 40 is briefly described.

In the liquid crystal display devices 40, voltage is applied to the gateelectrode 4 when the gate line 1 is selected. The voltage applied tothis gate electrode 4 controls a current to flow between the sourceelectrode 5 and the drain electrode 6. Then, current flows from thesource electrode 5 to the drain electrode 6, and from the drainelectrode 6 to the pixel electrode 3 through the lead out drainelectrode 6′, on the basis of the signal transmitted from the sourceline 2, and thereby, the pixel electrode 3 displays in a predeterminedmanner in the configuration. The auxiliary capacitor bus line 7 issecondarily installed to maintain the predetermined display in the pixelelectrode 3.

Next, an example of a manufacturing method for the active matrixsubstrate 30 according to the present embodiment is described withreference to FIGS. 2, 3 and 4.

In the manufacturing of the active matrix substrate 30 according to thepresent embodiment, the thin film transistor (TFT) 14 is formed. First,a layered film made of Ti/Al/Ti is formed by means of sputtering on theinsulating substrate 10 made of a transparent insulator, such as glass,and followed by photolithography, dry etching and removal of the resist,and thereby, the gate line 1, the gate electrode 4 and the commoncapacitance line 7 are simultaneously formed. Next, on top of thesurfaces of these, a gate insulator 11 made of an SiNx (silicon nitride)film having a thickness of approximately 4000 Å is formed using a mixedgas of an SiH₄ gas, an NH₃ gas and an N₂ gas, an active semiconductorlayer 12 made of amorphous silicon having a thickness of approximately1500 Å is formed using a mixed gas of an SiH₄ gas and an H₂ gas, and ann type low resistance semiconductor layer 13 into which phosphorous isdoped having a thickness of approximately 500 Å is formed using a mixedgas of an SiH₄ gas, a PH₃ gas and an H₂ gas, sequentially, according toCVD, followed by photolithography, dry etching and removal of theresist, so that an island form 25 is formed. Subsequently, a layeredfilm made of Ti/Al/Ti is formed by means of sputtering, followed byphotolithography and dry etching, so that the source line 2, the sourceelectrode 5, the drain electrode 6 and the lead out drain electrode 6′are simultaneously formed. Furthermore, the n type low resistancesemiconductor layer 13 is etched, so that the source and the drain areseparated from each other, and then, the resist is removed. In thismanner, the thin film transistor (TFT) 14 is formed.

Next, the lower interlayer insulation film 20 made of SiNx having athickness of approximately 3000 Å is formed so as to cover the entiresurface of the substrate according to CVD using a mixed gas of an SiH₄gas, an NH₃ gas and an N₂ gas. Subsequently, a film of SiNx having athickness of approximately 4000 Å is formed according to CVD using amixed gas of an SiH₄ gas, an NH₃ gas and an N₂ gas, followed byphotolithography and dry etching using a mixed gas of a CF₄ gas and anO₂ gas, and thereby, the protective film 8 is formed.

Then the upper layer organic insulating film 15 made of a positive typephotosensitive acryl resin having a thickness of approximately 3 μm isformed by means of photolithography so that the contact hole 9, thepattern for contact of terminals for leading out gate lines (X in FIG.16), and the pattern for contact of terminals for leading out sourcelines (Y in FIG. 17) is provided.

Next, in order to form the contact hole 9, terminal for leading out gateline 200 and terminal for leading out source line 300, the lowerinterlayer insulation film 20 and the gate insulator 11 are sequentiallyetched by means of dry etching using a mixed gas of a CF₄ gas and an O₂gas, and using the upper layer organic insulating film 15 as a mask.

After that, a transparent electrode is formed, by means of sputtering,so as to cover the entire surface of the substrate having the contacthole 9. Then, the formed transparent electrode is patterned by means ofphotolithography and wet etching so as to remove the resist, andthereby, the pixel electrode 3 is obtained.

In the present embodiment, Ti/Al/Ti is used as the material for the gateline 1 and the source line 2, but the material is not particularlylimited, as long as it is a metal that provides a desired lineresistance, for example, metals such as tantalum (Ta), titanium (Ti),chromium (Cr) and aluminum (Al), as well as alloys thereof, may be used.For the material of the gate line 1 and the source line 2, a film havinga layered structure of TaN/Ta/TaN may be used. And for the material ofthe source line 2, a transparent conductive film, such as ITO, forexample, may be used in addition to a general metal film.

In the present embodiment, an amorphous silicon thin film transistor isused as the switching element 14, a microcrystal silicon thin filmtransistor, a polysilicon thin film transistor and a CGS thin filmtransistor, for example, may be also used.

ITO is used for pixel electrode 3 in the present embodiment, atransparent electrode, such as one of IZO, may be used. And in the caseof a reflective type liquid crystal display devices, an electrodematerial that reflects light from the outside may be used as the pixelelectrode 3, and metals such as Al and Ag, for example, may be used.

A positive type acryl based photosensitive transparent resin is used forthe upper interlayer insulation film 15 in the present embodiment, butthe material is not particularly limited, as long as desired dielectricconstant, transmittance and etching selective ratio of the lowerinterlayer insulation film 15 to the gate insulator 11 are obtained, anda negative type photosensitive resin or an SiO₂ (silicon oxide) film,for example, may be used.

In the preset embodiment, an SiNx film according to a CVD method is usedas the lower interlayer insulation film 20, but a positive type ornegative type photosensitive transparent resin may be used. In addition,a photosensitive transparent resin, an SiO₂ film or the like may be usedin addition to an SiNx film, as the protective film 8. Examples of thephotosensitive transparent resin used for the lower interlayerinsulation film 20 and the protective film 8 include an acryl basedresin, an epoxy based resin, a polyurethane based resin and a polyimidebased resin.

Next, with reference to FIG. 4, described is the working effect of thepresent embodiment that no current leak occurs between the gate line 1and the pixel electrode 3 in the case of film defect on the upper layerorganic insulating film 15. FIG. 11 is a schematic plan diagram showingthe state of current leak at the leakage point 800 between the pixelelectrode and the gate line caused by peeling of the upper interlayerinsulation film in a previous active matrix substrate. FIG. 12 is aschematic cross sectional diagram showing a cross section of the leakagepoint 800 along line G-G′ of FIG. 11.

In the previous active matrix substrate 130, peeling of the upperinterlayer insulation film 115 (in the portion of the leakage point 800)due to a foreign substance involved when the upper interlayer insulationfilm 115 is applied as a film, or due to lack of adhesion at the time offilm application, as is clear from the above described manufacturingprocess, causes etching of the lower interlayer insulation film 120 andthe gate insulator 111 in the defect portion on the upper interlayerinsulation film 115. As a result, as shown in FIG. 12, the pixelelectrode 103 and the gate line 101 make contact with each other,resulting in a pixel defect due to electrical leakage, and causing thereduction in quality of the display and the yield.

According to the present invention, however, the protective film 8 isseparately formed of an insulating material on the gate line 1, andtherefore, the gate line 1 may be protected against etching when etchingis carried out using the upper interlayer insulation film 15 as a mask,and the protective film 8 remains between the pixel electrode 3 and thegate line 1 so that the working effect of preventing pixel loss isgained. Specifically, SiNx having a total thickness of approximately7000 Å is etched in a process where the lower interlayer insulation film20 made of SiNx having a thickness of approximately 3000 Å and the gateinsulator 11 made of SiNx having a thickness of approximately 4000 Å areetched using the upper interlayer insulation film 15 as a mask, however,addition of SiNx having a thickness of approximately 4000 Å as theprotective film 8, permits the sufficient film thickness (substantially11000 Å in total) of the SiNx film in the portion where the protectivefilm 8 has been formed, and therefore, contact between the gate line 1and the pixel electrode 3 may be sufficiently prevented.

Embodiment 2

Embodiment 2, which is another embodiment according to the presentinvention, is described below, with reference to FIGS. 5 to 7. For thepurpose of convenience of description, the same symbols are attached tomembers having the same functions as those shown in the drawings ofEmbodiment 1, and the descriptions thereof are omitted.

According to Embodiment 2, a protective layer is formed together with asemiconductor layer to form a switching element (TFT), and after that,is separated from the semiconductor layer of the switching element, soas to have a configuration not overlapping the source lines. An activematrix substrate (substrate for a display device) according toEmbodiment 2, where such a protective layer (hereinafter referred toalso as a protective semiconductor layer), is provided, is describedwith reference to FIGS. 5 to 7.

FIG. 5 is a schematic plan diagram showing one element in the activematrix substrate 30 according to the present invention. FIG. 6 is across sectional diagram showing the substrate for a display device alongline C-C′ of FIG. 5, and FIG. 7 is a cross sectional diagram of thesubstrate for a display device along line D-D′ of FIG. 5.

First, an example of a manufacturing method for the active matrixsubstrate 30 according to the present embodiment is described. In themanufacturing of the active matrix substrate 30 according to the presentembodiment, the thin film transistor (TFT) 14 is formed. First, the gateline 1, the gate electrode 4 and the common capacitance line 7 areformed on the insulating substrate 10 made of a transparent insulator,such as glass, in the same process. Next, on top of the surfaces ofthese, the gate insulator 11 made of SiNx having a thickness ofapproximately 4000 Å is formed using a mixed gas of an SiH₄ gas, an NH₃gas and an N₂ gas, the active semiconductor layer 12 made of amorphoussilicon having a thickness of substantially 1500 Å is formed using amixed gas of an SiH₄ gas and an H₂ gas, and the n type low resistancesemiconductor layer 13 having a thickness of approximately 500 Å intowhich phosphorous has been doped is formed using a mixed gas of an SiH₄gas, a PH₃ gas and an H₂ gas, sequentially, by means of CVD, followed byphotolithography, dry etching and removal of the resist, and thus, anisland 25 is formed. At this time, the protective semiconductor layer 26is simultaneously formed. Furthermore, a film formation,photolithography and dry etching are carried out so as to simultaneouslyform the source line 2, the source electrode 5, the drain electrode 6and the lead out drain electrode 6′. Furthermore, sources and drains areseparated from the n type low resistance semiconductor layer 13 throughetching, and then, the resist is removed. In this manner, the thin filmtransistor (TFT) 14 is formed.

Then the lower interlayer insulation film 20 made of SiNx having athickness of approximately 3000 Å is formed using a mixed gas of an SiH₄gas, an NH₃ gas and an N₂ gas by means of CVD, so as to cover the entiresurface of the substrate. After that, the upper layer organic insulatingfilm 15 made of a positive type photosensitive acryl resin having athickness of approximately 3 μm is formed by means of photolithographyso as to have the contact hole 9, the pattern for contacts of terminalsfor leading out gate line (X of FIG. 16), and the pattern for contactsof terminals for leading out source line (Y of FIG. 17).

Then the lower interlayer insulation film 20 and the gate insulator 11are sequentially etched by means of dry etching using a mixed gas of aCF₄ gas and an O₂ gas, using the upper layer organic insulating film 15as a mask, in order to form the contact hole 9, terminal for leading outgate line 200 and terminal for leading out source line 300.

After that, a transparent electrode is formed by means of sputtering, soas to cover the entire surface of the substrate having the contact hole9. Next, the transparent electrode that has been formed is patterned bymeans of photolithography and wet etching, and then, the resist isremoved, and thereby, a pixel electrode 3 is obtained.

Next, with reference to FIG. 7, described is the working effect of thepresent embodiment that no current leak occurs between the gate line 1and the pixel electrode 3 in the case of film defect on the upper layerorganic insulating film 15. In the previous active matrix substrate,peeling of the upper interlayer insulation film due to a foreignsubstance involved when the upper interlayer insulation film is appliedas a film, or due to lack of adhesion at the time of film application,as is clear from the above manufacturing process, causes etching of thelower interlayer insulation film and the gate insulator in the defectportion on the upper interlayer insulation film. As a result, as shownin FIG. 12, the pixel electrode 103 and the gate line 101 make contactwith each other, resulting in a pixel defect due to electrical leakage,and causing the reduction in quality of the display and the yield.

According to the present invention, however, the protectivesemiconductor layer 26 is separately formed on the gate line 1, andtherefore, the gate line 1 may be protected against etching at the timewhen etching is carried out using the upper interlayer insulation film15 as a mask, and the protective semiconductor layer 26 remains betweenthe pixel electrode 3 and the gate line 1, and thus, the working effectsof preventing the occurrence of a pixel defect may be obtained.Specifically, SiNx having a total thickness of approximately 7000 Å isetched in the process of etching the lower interlayer insulation film 20made of SiNx having a thickness of approximately 3000 Å, and the gateinsulator 11 made of SiNx having a thickness of approximately 4000 Åusing the upper interlayer insulation film 15 as a mask, but theprotective semiconductor layer 26 has a film thickness of approximately1500 Å and the etching selective ratio of SiNx to the protectivesemiconductor layer 26 is approximately 1:10 at the time when SiNx isetched using a mixed gas of a CF₄ gas and an O₂ gas, and therefore, asufficient amount of remaining film of the gate insulator 11 may besecured, and the contact between the gate line 1 and the pixel electrode3 may be sufficiently prevented.

According to the present embodiment, the protective semiconductor layer26 is formed together with the semiconductor layer to form the switchingelement (TFT) 14, and therefore, shortening of the process as comparedwith Embodiment 1 may be achieved.

Furthermore, according to the present embodiment, the protectivesemiconductor layer 26 and the semiconductor layer that forms theswitching element (TFT) 14 are separated and do not overlap the sourceline 2 in the configuration, and therefore, the protective semiconductorlayer 26 that is provided on the gate line (scan line) and the sourceline (signal line) 2 which is adjacent to the switching element 14 andis connected to the switching element 14 can be prevented from causingelectrical leakage to the drain electrode 6 that is connected to theswitching element 14, even in the case where leakage occurs betweenthese, and therefore, a pixel defect may be prevented.

Embodiment 3

Embodiment 3, which is another embodiment according to the presentinvention, is described below, with reference to FIGS. 8 to 10. And forthe purpose of convenience of description, the same symbols are attachedto members having the same functions as those shown in the drawingsconcerning Embodiments 1 and 2, and the descriptions thereof areomitted.

The configuration according to Embodiment 3 is characterized in that aprotective semiconductor layer is disposed least in portions where thegate lines (scan lines) and the pixel electrode overlap as viewed in thedirection perpendicular to the surface of the insulating substrate inthe configuration of Embodiment 2. The active matrix substrate 30according to Embodiment 3 where such a protective semiconductor layer isprovided is described with reference to FIGS. 8 to 10.

FIG. 8 is a schematic plan diagram showing one pixel in the activematrix substrate 30 according to the present invention.

FIG. 9 is a cross sectional diagram showing the substrate for a displaydevice along line E-E′ of FIG. 8, and FIG. 10 is a cross sectionaldiagram showing the substrate for a display device along line F-F′ ofFIG. 8.

First, an example of a manufacturing method for the active matrixsubstrate 30 according to the present embodiment is described. In themanufacturing of the active matrix substrate 30 according to the presentembodiment, the thin film transistor (TFT) 14 is formed. First, the gateline 1, the gate electrode 4 and the common capacitance line 7 areformed on the insulating substrate 10 made of a transparent insulator,such as glass, in the same process. Next, on top of the surfaces ofthese, the gate insulator 11 made of SiNx having a thickness ofapproximately 4000 Å is formed using a mixed gas of an SiH₄ gas, an NH₃gas and an N₂ gas, the active semiconductor layer 12 made of amorphoussilicon having a thickness of approximately 1500 Å is formed using amixed gas of an SiH₄ gas and an H₂ gas, and the n type low resistancesemiconductor layer 13 having a thickness of approximately 500 Å intowhich phosphorous has been doped is formed using a mixed gas of an SiH₄gas, a PH₃ gas and an H₂ gas, sequentially, by means of CVD, followed byphotolithography, dry etching and removal of the resist, and thus, theisland 25 is formed. At this time, the protective semiconductor layer 26is simultaneously formed. Furthermore, a film formation,photolithography and dry etching are carried out so as to simultaneouslyform the source line 2, the source electrode 5, the drain electrode 6and the lead out drain electrode 6′. Furthermore, in a sequentialprocess, sources and drains are separated from the n type low resistancesemiconductor layer 13 through etching, and then, the resist is removed.In this manner, the thin film transistor (TFT) 14 is formed.

Then the lower interlayer insulation film 20 made of SiNx having athickness of approximately 3000 Å is formed using a mixed gas of an SiH₄gas, an NH₃ gas and an N₂ gas by means of CVD, so as to cover the entiresurface of the substrate. After that, the upper layer organic insulatingfilm 15 made of a positive type photosensitive acryl resin having athickness of approximately 3 μm is formed by means of photolithographyso as to have the contact hole 9, the pattern for contacts of terminalsfor leading out gate line (X of FIG. 16), and the pattern of contactsfor terminals for leading out source line (Y of FIG. 17).

Then the lower interlayer insulation film 20 and the gate insulator 11are sequentially etched by means of dry etching using a mixed gas of aCF₄ gas and an O₂ gas, using the upper layer organic insulating film 15as a mask, in order to form the contact hole 9, terminal for leading outgate line 200 and terminal for leading out source line 300.

After that, a transparent electrode is formed by means of sputtering, soas to cover the entire surface of the substrate having the contact hole9. Next, the transparent electrode that has been formed is patterned bymeans of photolithography and wet etching, and then, the resist isremoved, and thereby, the pixel electrode 3 is obtained.

Next, with reference to FIG. 10, described is the working effect of thepresent embodiment that no current leak occurs between the gate line 1and the pixel electrode 3 in the case of film defect on the upper layerorganic insulating film. In the previous active matrix substrate,peeling of the upper interlayer insulation film due to a foreignsubstance involved when the upper interlayer insulation film is appliedas a film, or due to lack of adhesion at the time of film application,as is clear from the above manufacturing process, causes etching of thelower interlayer insulation film and the gate insulator in the defectportion on the upper interlayer insulation film. As a result, as shownin FIG. 12, the pixel electrode 103 and the gate line 101 make contactwith each other, resulting in a pixel defect due to electrical leakage,and causing the reduction in quality of the display and the yield.

According to the present invention, however, the protectivesemiconductor layer 26 is separately formed on the gate line 1, andtherefore, the gate line 1 may be protected against etching at the timewhen etching is carried out using the upper interlayer insulation film15 as a mask, and the protective semiconductor layer 26 remains betweenthe pixel electrode 3 and the gate line 1, and thus, the working effectsof preventing the occurrence of a pixel defect may be obtained.Specifically, SiNx having a total thickness of approximately 7000 Å isetched in the process of etching the lower interlayer insulation film 20made of SiNx having a thickness of approximately 3000 Å, and the gateinsulator 11 made of SiNx having a thickness of approximately 4000 Åusing the upper interlayer insulation film 15 as a mask, but theprotective semiconductor layer 26 has a film thickness of approximately1500 Å and the etching selective ratio of SiNx to the protectivesemiconductor layer 26 is approximately 1:10 at the time when SiNx isetched using a mixed gas of a CF₄ gas and an O₂ gas, and therefore, asufficient amount of remaining film of the gate insulator 11 may besecured, and the contact between the gate line 1 and the pixel electrode3 may be sufficiently prevented.

In addition, the active matrix substrate (substrate for a displaydevice) 30 according to the present Embodiment is characterized in thatthe protective semiconductor layer 26 is disposed at least atintersections of the gate lines (scanlines) 1 and the pixel electrodes 3as viewed in the direction perpendicular to the surface of theinsulating substrate 10 in the configuration of Embodiment 2, and insuch a configuration, an increase in the load capacitance of the gatelines 1 may be restricted to the minimum, and may be more restricted inthe case where the protective semiconductor layer 26 is provided so asto completely cover the gate lines 1.

The protective film 8 (protective semiconductor layer 26) is providedonly on the gate lines 1 according to the above described Embodiments 1to 3, but the protective film (protective semiconductor layer) may beprovided to the auxiliary capacitance lines 7 in the same manner, andthereby, an effect of preventing current leakage between the auxiliarycapacitance line 7 and the pixel electrode 3 may be obtained, accordingto the present invention.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. A substrate for a display device comprising: a scan line; a signalline; a switching element provided on an insulating substrate; aninterlayer insulation film; and a pixel electrode; wherein saidswitching element is provided at an intersection of the scan line andthe signal line; said switching element includes a gate electrodeconnected to the scan line, a source electrode connected to the signalline, and a drain electrode connected to the pixel electrode; saidinterlayer insulation film includes a contact hole for connecting thedrain electrode of the switching element to the pixel electrode; aprotective layer formed of an insulating material is provided withoutcontact holes above the scan line and/or the signal line; and a portionof an underlying film under the protective layer contacts a portion ofan overlying film over the protective layer.
 2. The substrate for adisplay device according to claim 1, wherein said protective layer isprovided beneath the interlayer insulation film.
 3. The substrate for adisplay device according to claim 1, wherein said protective layer isprovided at least in a portion where the scan line and the pixelelectrode overlap as viewed in a direction perpendicular to a surface ofthe insulating substrate.
 4. The substrate for a display deviceaccording to claim 1, wherein said protective layer prevents the scanline and/or the signal line from being exposed through the contact hole.5. The substrate for a display device according to claim 1, wherein saidprotective layer is provided substantially directly above the scan lineand/or the signal line.
 6. The substrate for a display device accordingto claim 1, wherein said protective layer is provided along the lines ofthe scan line and/or the signal line.
 7. The substrate for a displaydevice according to claim 1, wherein said protective layer is providedat an overlap region of the scan line and/or the signal line and thepixel electrode.
 8. A display device, comprising the substrate for adisplay device according to claim
 1. 9. A substrate for a display devicecomprising: a scan line; a signal line; a common capacitance wiring; aswitching element provided on an insulating substrate; an interlayerinsulation film; and a pixel electrode; wherein said switching elementis provided at the intersection of the scan line and the signal line;said switching element includes a gate electrode connected to the scanline, a source electrode connected to the signal line, and a drainelectrode connected to the pixel electrode; said interlayer insulationfilm includes a contact hole for connecting the drain electrode of theswitching element to the pixel electrode; a protective layer formed ofan insulating material is provided without contact holes above at leastone of wirings selected from the group consisting of the scan line, thesignal line, and the common capacitance wiring; and a portion of anunderlying film under the protective layer contacts a portion of anoverlying film over the protective layer.
 10. The substrate for adisplay device according to claim 9, wherein said protective layer isprovided beneath the interlayer insulation film.
 11. The substrate for adisplay device according to claim 9, wherein said protective layer isprovided at least in a portion where the scan line and the pixelelectrode overlap as viewed in the direction perpendicular to a surfaceof the insulating substrate.
 12. The substrate for a display deviceaccording to claim 9, wherein said protective layer prevents at leastone of wirings selected from the group consisting of the scan line, thesignal line, and the common capacitance wiring from being exposedthrough the contact hole.
 13. The substrate for a display deviceaccording to claim 9, wherein said protective layer is providedsubstantially directly above at least one of wirings selected from thegroup consisting of the scan line, the signal line, and the commoncapacitance wiring.
 14. The substrate for a display device according toclaim 9, wherein said protective layer is provided along the lines of atleast one of wirings selected from the group consisting of the scanline, the signal line, and the common capacitance wiring.
 15. Thesubstrate for a display device according to claim 9, wherein saidprotective layer is provided at an overlap region of at least one ofwirings selected from the group consisting of the scan line, the signalline, and the common capacitance wiring and the pixel electrode.
 16. Adisplay device, comprising the substrate for a display device accordingto claim 9.